The present invention relates to compositions based on vinylidene fluoride polymers, which have a reduced smoke-producing capacity.
Vinylidene fluoride polymers are inflammable with difficulty and are self-extinguishable. The incorporation into them, before they are used, of flame retardants such as certain specific compounds of tin, with a view to further improving their fire-resistance, has already been proposed. Nevertheless, flame retardants have generally proved to be unsuitable for preventing totally the combustion of shaped articles made of vinylidene fluoride polymers, at high temperature.
Moreover, reducing the smoke-producing capacity, i.e. the capacity to generate smoke by combustion, and ignition delay of a polymer composition are two different phenomena which are not directly related to each other, to such an extent that some flame retardant compounds act, in some cases, as smoke producers, once the combustion has effectively started, or that some smoke reducers induce, in some cases, incandescence phenomena which promote ignition.
In contrast to the generally held view, it is now known that the combustion of shaped articles made of vinylidene fluoride polymers causes smoke to be produced in a quantity sufficient to form a disadvantage as serious as the flames themselves, insofar as it makes the control of fire more difficult.
The use of molybdenum derivatives, such as metal molybdates, in order to reduce effectively the quantity of smoke emitted during the combustion of vinylidene fluoride polymers is described in French Patent FR-A-82/17,123 (SOLVAY & Cie). However, the incorporation of metal molybdates into vinylidene fluoride polymers leads to an opaquing of the shaped articles, thereby decreasing the possibilities of use in some fields of use in which a high transparency is required, such as, for example, coating electric cables.